Preserving Plastics

It probably comes as no real surprise that 100-year-old oil paintings like those in the Fitzwilliam Museum might need conserving, but conservators are also finding that more modern materials like plastic are also degrading. We spoke to Anita Quye who's a lecturer in conversation science from the University of Glasgow to find out whether this is just a modern problem.

Anita - Well, it's quite interesting. It's been going on for about 30 or so years. In the late '80s, people were starting to notice that some plastics maybe weren't surviving quite as long as we might have expected them to. They were starting to do odd things. They were starting to crack up, they were starting to weep, which sounds a bit extreme, but they were giving out liquids. And so, there's quite a concerted effort from that period on and it's escalating now. More and more people internationally are collaborating to look into the chemical reasons to why these materials are starting to degrade.

Chris - Because of course, we're all brought up and told, plastic is really bad because if it goes into a landfill, it's going to last a million years before it breaks down and it soils the environment, and these things last forever. But actually, that isn't true and also, by the sound of it - what you're saying - there is a lot of it about that is in need of preserving because it became so ubiquitous and people don't regard it as very important.

Anita - Absolutely. Plastics, for their absolutely fascinating and perhaps quite a remarkably long history behind them, I think most people maybe think of plastics being things like PVC which you might associate to be like the 1940s and post-World War 2 chemical efforts from that. But it actually goes back a lot earlier. We're talking about the 1860s.

我们讨论的时间艺术和三英洁具ce really were coming together to create these new man-made materials. And the ironic thing behind is that a lot of these early synthetic plastics which were appearing in the Victorian period and becoming quite novel materials were based on natural polymers, things like cellulose and paper, and cotton, were being chemically modified to create some of these early ones. People might have heard of celluloid for example, which is cellulose nitrate. And then by the early 20^thcentury, scientists were starting to take these plastics that you could mould, that you could make into films and starting to make fibres from them.

So, the very first synthetic fibre was something called rayon which people might be familiar with and that's where you take that natural cellulose polymer and you break the cotton polymer down and then you regenerate it again, and you can control the length of the polymer chains, and you can make a much better fibre from it. So, we're talking about collections that people might not associate with plastics and the materials have gone from being this novel material first of all. By the 1940s, becoming a very utilitarian and very much a futuristic look at what we can do - this is the future guy's - kind of material. So then, by the time it gets the 1960s and they start to get a slightly different kind of imagery behind them - they're disposable, they're not long lasting. So, it's gone through this wave of being a novelty to being something that's disposable and I think that's lasted with us today and now, like you say, the environmental issues that are behind them. But they are misbehaving and they're starting to degrade and...

Chris - But chemically, what underlies that degradation because most people regard plastics as relatively inert or stable? So, what's going on inside the plastic to make it do that?

安妮塔,当塑料——所以,these are very early ones, the cellulose nitrates, the cellulose acetates, we found through some research that we've been doing is that the actual way that you make the plastic is actually unfortunately a misfortune. So, when - like I say, you take the cellulose and you treat it with acids for example, and part of the process, whether you're making cellulose nitrate or cellulose acetate, is you create a cellulose sulphate as an intermediate and then you can control this nitration or acetylation process much more in a controlled fashion. And we found that certain levels, about 5mg of sulphate remaining in the plastic - per gram of plastic - is enough to indicate that that particular material is either degrading or has a potential to degrade. Then there are things like the PVCs for example, PVC, we might recognise it in our homes, in our window frames for example, you can get U-PVC window frames and that's a very hard material. But manufacturers can add in plasticisers to make that into a PVC plastic bag for example which you might be familiar with, as a carrier bag. So, you can get these formulations where you're introducing chemicals into them and over decades, over centuries, you're now starting to get these materials moving within the plastic. So PVCs for example nowadays, some of the old ones are degrading is because the plasticiser is moving through the plastic and appearing as a sticky liquid on the surface.

Chris - Can we reverse these changes?

安妮塔——好问题。我认为如果我们问一个聚合物scientist, the first thing that they normally respond to is, "well, why don't you just coat everything? Why don't you try and re-introduce these plasticisers again?" But I think Oliver mentioned actually about reversibility - something that when it comes to preservation of collections, we're trying to be as hands off as possible. So, we're trying to control environments, trying to control humidity and temperature which has an impact on how these materials behave. But we're actually a little bit cautious nowadays about coating things or trying to change the material back. Certainly, from a chemical point of view, once these degradation processes happen, you can't chemically change them back. The amount of energy that you need is very difficult to re-introduce. And from a conservation point of view, to start interfering with the materials, starting to put another material onto it can have devastating effects. And unfortunately, through textile conservation, we found that there was a great love of using soluble nylon as an adhesive for adhering support fabrics onto things like tapestries in the 1960s and '70s and the nylon material at that time was very reversible and you could take it back off with a solvent. But nowadays, it's polymerised and it's become hardened, and it's almost irreversible to remove it. So, there's a great deal of wariness about doing that kind of interventive treatment at the moment.

Chris - So, is it curtains, Anita, for some things that we have in our museums, are we going to see them disappear because we just do not have the ability to preserve these plastics because they will inexorably degrade?

Anita - Yes. We're getting to that point now I think where we're just faced with more and more things coming to our collections that we're having to make decisions and it's a big wide issue. Again, a mountain will be eroding but very slowly. Some materials in our collections nowadays are doing similar changes, but they're happening over a much faster period than we can imagine. So, we're going to have to start making some decisions about them and unfortunately, we don't think we'll be able to keep everything. Museums are constrained economically and have to think carefully about their collections too, but to conservation, we're doing our absolute best that we can in collaboration with scientists around the world.